It is well known that fermentable yeasts are used in the preparation of alcoholic beverages. The enzymes occurring in the corresponding yeasts act to break down one or more substances (for example, fermentable sugar in beer wort, grape must, or distillery mash), and to, at least partly, convert the substances into ethyl alcohol. This latter function is notable because of the use of alcohol as a semiluxury food substance, as a chemical raw material, and as fuel for combustion engines.
Unfortunately, the yeasts employed are not always sufficiently equipped with enzymes for engaging in all desired reactions. Wine yeasts, for example, possess only insufficient protein-splitting activity, so that proteins in the must are degradated only on a small scale. This may lead to a foaming over of the fermenting batches as well as to considerable clarification and stability difficulties in wines, which can only be remedied by additional application of, for example, bentonite or other fining agents such as, for example, gelatin or silicasol.
Also, it has not previously been possible to attenuate, i.e., ferment, the trisaccharide raffinose occurring in many raw materials of the distillery with the usual distilling yeasts and top-fermented brewery yeasts of the Saccharomyces cerevisiae type. Since .alpha.-galactosidase (melibiase) is missing in these yeasts, only one-third of the raffinose is attenuated; the remaining two-thirds of the raffinose consisting of melibiose occurring in beer wort or molasses, remains unused, so that the alcohol yield remains under its theoretically possible value.
For brewery practice with bottom and also top-fermented brewers yeasts (Saccharomyces uvarum and carlsbergensis or Saccharomyces cerevisiae, respectively) it is disadvantageous that these types of yeast have practically no .beta.-glucanase by nature, so that .beta.-glucanes are not split and cause difficulties with the subsequent filtering of the beer. Analogous conditions prevail due to the lack of pectinases in wine yeasts (Saccharomyces cerevisiae, Saccharomyces bayanus).
It has already been known, or has at least suggested in the prior art, to add to a fermenting batch all those enzymes which the yeast within the fermenting batch does not contain. Thus, soluble .beta.-glucanases are used, for example, to obtain a sufficient glucane degradation in beer. In wine production soluble pectinases have already been used. These methods, however, have the disadvantage, that the finished beverage, for example, beer or wine, still contains the enzyme protein. Further shortcomings in the use of soluble enzymes include, for example, the situation such as that of soluble pepsin and its only insufficient activity in foam suppression in must attenuation.
When known immobilized enzymes are used, the final product, for example, beer or wine, may be kept free from enzyme protein; however, these preparations--when added to the fermenting batch in addition to the yeast--do not lead to the desired success of a quick degradation of the substance not degradable by the fermenting yeast if the fermentation batch is not stirred intensely by means of a stirrer. Thus, successful employment of the known immobilized preparations demands additional technical expenditure, which may cause considerable difficulties and is not practical in many applications (such as breweries, distilleries, or wine producers). Often the use of known immobilized preparations is precluded by harmful side-effects, such as, for example, undesired addition of oxygen and excessive growth of yeast.
In addition, it has already been known from works by Y. Takasaki that enzymes can be bound to cells of microorganisms. U.S. Pat. No. 3,950,220 as well as Agr. Biol. Chem., 38, 1081-1082 (1974), furnish details on the subject. The process disclosed by Takasaki is suitable for mold fungi, but it is unsuitable for fermenting yeast cells as it leads to complete inactivation of the fermenting enzyme system of the cells. Furthermore, it has the drawback that only relatively few enzyme proteins can be bound to one cell, and thus, the specific enzyme activity of these preparations is insignificant.
The above-mentioned disadvantage of a small enzyme coverage on the enzyme-cell co-immobilisates is remedied by a new method by B. Hagerdal and K. Mosbach (Abstracts for the Food Process Engineering Congress, Helsinki, 1979), where .beta.-glucosidase in alginate gel is wrapped around the cells. This method will work with living, fermentable yeast cells; however, there is the drawback that very big enzyme yeast cell particles are formed, so that the usual floating capacity of the yeast cells in media to be attenuated (mash, wort, must, and similar ones) is diminished and considerable decreases of the fermentation output occur. A further disadvantage is the increased resistance to diffusion which the relatively thick enzyme-alginate layer provides against the passing of fermentable substances towards the yeast cell.